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Inversion efficiency model yields improved accuracy in MP2RAGE-based T1-mapping in the human brain at 7.0T

Olsson, Hampus ; Opheim, Jan Ole ; Andersen, Mads LU ; Herrman, Carl ; Lutz, Max ; Waiczies, Sonia ; Niendorf, Thoralf and Helms, Gunther LU orcid (2025) In NMR in Biomedicine 38(7).
Abstract
Introduction:
Estimation of the longitudinal relaxation time T1 from the MP2RAGE pulse sequence is based on a monoexponential signal evolution model. However, magnetization transfer caused by the inversion pulse induces a fast relaxation component which appears as a reduction in the efficiency of the inversion. This may explain the underestimation of T1 derived from MP2RAGE. To address this systematic bias, an “apparent” inversion efficiency (finv) was introduced which comprises all mechanisms that affect the inversion in the monoexponential MP2RAGE signal model. The MP2RAGE model was then extended by calibrating an empirical linear dependence of finv on R1=1/T1, resulting in increased accuracy of the estimated T1.... (More)
Introduction:
Estimation of the longitudinal relaxation time T1 from the MP2RAGE pulse sequence is based on a monoexponential signal evolution model. However, magnetization transfer caused by the inversion pulse induces a fast relaxation component which appears as a reduction in the efficiency of the inversion. This may explain the underestimation of T1 derived from MP2RAGE. To address this systematic bias, an “apparent” inversion efficiency (finv) was introduced which comprises all mechanisms that affect the inversion in the monoexponential MP2RAGE signal model. The MP2RAGE model was then extended by calibrating an empirical linear dependence of finv on R1=1/T1, resulting in increased accuracy of the estimated T1.
Methods:
The apparent inversion efficiency finv and the apparent T1* (yielding T1 by auxiliary B1+-mapping) were mapped at 7T in healthy adults using phase-sensitive inversion recovery (IR) with four consecutive RAGE trains (PS-MP4RAGE) in conjunction with adiabatic inversion using time resampled (TR) -FOCI and hyperbolic secant pulses. Upon validation by conventional IR-EPI, PS-MP4RAGE was used to calibrate the linear finv model for the human brain. These 3D T1 maps also served as a reference to assess the improvement of the MP2RAGE-based T1 estimates.
Results:
The apparent inversion efficiency finv was consistently smaller in white matter (WM) than in gray matter (~0.73 vs ~0.84). The difference in WM T1 between MP2RAGE and the reference PS-MP4RAGE technique was reduced by more than 200 ms when using the suggested finv model.
Discussion:
Magnetization transfer (MT) effects after spin inversion in MP2RAGE can be accounted for by calibrating the apparent inversion efficiency finv without introducing additional parameters. The proposed empirical model retains the B1+ compensation inherent to MP2RAGE and facilitates accurate T1 quantification in brain tissue. (Less)
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author
; ; ; ; ; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
human brain, parametric mapping, T1 quantification, 7T, MP2RAGE
in
NMR in Biomedicine
volume
38
issue
7
article number
e70067
publisher
John Wiley & Sons Inc.
ISSN
1099-1492
DOI
10.1002/nbm.70067
language
English
LU publication?
yes
id
30118282-ec11-4336-a03d-7d25c0c303a2
date added to LUP
2025-05-13 10:38:34
date last changed
2025-06-16 07:28:16
@article{30118282-ec11-4336-a03d-7d25c0c303a2,
  abstract     = {{Introduction: <br/>Estimation of the longitudinal relaxation time T1 from the MP2RAGE pulse sequence is based on a monoexponential signal evolution model. However, magnetization transfer caused by the inversion pulse induces a fast relaxation component which appears as a reduction in the efficiency of the inversion. This may explain the underestimation of T1 derived from MP2RAGE. To address this systematic bias, an “apparent” inversion efficiency (finv) was introduced which comprises all mechanisms that affect the inversion in the monoexponential MP2RAGE signal model. The MP2RAGE model was then extended by calibrating an empirical linear dependence of finv on R1=1/T1, resulting in increased accuracy of the estimated T1. <br/>Methods:<br/>The apparent inversion efficiency finv and the apparent T1* (yielding T1 by auxiliary B1+-mapping) were mapped at 7T in healthy adults using phase-sensitive inversion recovery (IR) with four consecutive RAGE trains (PS-MP4RAGE) in conjunction with adiabatic inversion using time resampled (TR) -FOCI and hyperbolic secant pulses.  Upon validation by conventional IR-EPI, PS-MP4RAGE was used to calibrate the linear finv model for the human brain. These 3D T1 maps also served as a reference to assess the improvement of the MP2RAGE-based T1 estimates.<br/>Results: <br/>The apparent inversion efficiency finv was consistently smaller in white matter (WM) than in gray matter (~0.73 vs ~0.84). The difference in WM T1 between MP2RAGE and the reference PS-MP4RAGE technique was reduced by more than 200 ms when using the suggested finv model. <br/>Discussion:<br/>Magnetization transfer (MT) effects after spin inversion in MP2RAGE can be accounted for by calibrating the apparent inversion efficiency finv without introducing additional parameters. The proposed empirical model retains the B1+ compensation inherent to MP2RAGE and facilitates accurate T1 quantification in brain tissue.}},
  author       = {{Olsson, Hampus and Opheim, Jan Ole and Andersen, Mads and Herrman, Carl and Lutz, Max and Waiczies, Sonia and Niendorf, Thoralf and Helms, Gunther}},
  issn         = {{1099-1492}},
  keywords     = {{human brain; parametric mapping; T1 quantification; 7T; MP2RAGE}},
  language     = {{eng}},
  month        = {{05}},
  number       = {{7}},
  publisher    = {{John Wiley & Sons Inc.}},
  series       = {{NMR in Biomedicine}},
  title        = {{Inversion efficiency model yields improved accuracy in MP2RAGE-based T1-mapping in the human brain at 7.0T}},
  url          = {{https://lup.lub.lu.se/search/files/220551024/NMR_in_Biomedicine_-_2025_-_Olsson_-_Inversion_Efficiency_Model_Yields_Improved_Accuracy_in_MP2RAGE_Based_T1_Mapping_in_the.pdf}},
  doi          = {{10.1002/nbm.70067}},
  volume       = {{38}},
  year         = {{2025}},
}